Over the past 40 years, considerable progress has been made in understanding mechanisms of vestibular function. One major advance has been the recognition that vestibular primary afferents are structurally and physiologically heterogeneous; unfortunately, the functional significance of this diversity remains unclear. A central issue is the fate of afferent signals when they reach the CNS: how do different afferents modulate the activity of central vestibular neurons, and how do these effects depend on the nature of the stimulus? I propose to address this question through simultaneous extracellular recordings from (1) single vestibular nucleus neurons and (2) their eighth nerve afferents in an in vitro preparation of the turtle brainstem. Dynamic afferent stimulation will be provided by sinusoidally modulated currents delivered to the posterior canal. This approach will allow me to: 1) quantify the contribution of individual vestibular afferents to the discharge of secondary neurons; 2) quantify patterns of convergence of vestibular afferents with different functional properties onto individual secondary neurons; 3) quantify the dynamics of signal transmission across the synapse and any changes that occur as a function of stimulus properties. This R21 application seeks funding to establish the feasibility of my dual recording preparation and to conduct pilot studies on synaptic transmission at the first central vestibular synapse. Once these aims are accomplished I will be positioned to pursue my long-term objective: to learn how synaptic transmission between afferents and vestibular nucleus neurons varies as a function of afferent type and the nature of the afferent stimulus.